Morphology of the coracoid process as a predictor of articular-side tear at the upper border of the subscapularis

Articular-side tear at the upper border of the subscapularis (SSC-AST) is often detected during shoulder arthroscopic surgery, although its exact pathology remains unknown. The purpose of this study was to investigate the correlation between various characteristics of the coracoid process, including classification of the morphology of the coracoid process tip, and the presence of SSC-AST.This retrospective, case-controlled study included patients who underwent arthroscopic subacromial decompression with or without rotator cuff repair between January 2018 and September 2021. A total of 130 shoulders in 124 patients, including 77 male and 53 female shoulders (mean age at surgery, 64 years [range, 39-88 years]), were included in this study. Three-dimensional (3D) computed tomography examination was performed preoperatively, and the following indices were measured: coracoid proximal length, coracoid distal length, coracoid angle, coracoglenoid angle, offset of the coracoid process and glenoid (anterior, lateral, and superior offset), and coracoid base angle. The morphology of the tip of the coracoid process was classified into 3 types according to 3D reconstructed views: flat type, round type, and beak type. The presence of SSC-AST was intraoperatively evaluated arthroscopically via a posterior glenohumeral portal. Morphologic risk factors for SSC-AST were evaluated between SSC-AST cases (group T) and non-SSC-AST cases (group N) by multivariable logistic analysis. In addition, the correlation between the incidence of SSC-AST and classification of the tip of the coracoid process was analyzed.SSC-AST was present in 53 shoulders (40.8%). Group T patients were significantly older than group N patients (68.4 ± 10.0 years vs. 61.5 ± 11.8 years, P < .001). No sex difference was detected between the 2 groups (28 male and 25 female shoulders in group T vs. 49 male and 28 female shoulders in group N, P = .28). Multivariate analysis of morphologic parameters between the 2 groups detected a smaller superior offset as a risk factor for SSC-AST (odds ratio, 0.91; 95% confidence interval, 0.84-0.98; P = .01). No significant differences were found in the other parameters. Regarding classification of the tip of the coracoid process, round- and beak-type coracoid tips had a significantly higher rate of SSC-AST than flat-type tips (flat type, 21.8%; round type, 64.7%; and beak type, 46.3%) (P < .001).Evaluation of the correlation between the morphology of the coracoid process on 3D computed tomography and the presence of SSC-AST visualized during arthroscopy indicated a significant association between SSC-AST and the morphology of the coracoid process.